Recently, in the field of displays such as televisions including liquid crystal panels, as an approach to achieve higher performance, 3D displays with which 3D images can be enjoyed have been developed. In such 3D displays, a stereoscopic image can be displayed by, for example, making the right eye of a viewer see an image for the right eye and making the left eye of the viewer see an image for the left eye.
Various 3D display methods for displaying 3D images can be used, and examples of the methods known as methods requiring no special eyeglasses include a lenticular lens method and a parallax barrier method.
As one of display methods for viewers to see 3D images with eyeglasses, a circularly polarized glasses method, for example, is known (see Patent Document 1, for example).
In a 3D display using the circularly polarized light glasses method, a retardation material is generally arranged on a display element, such as a liquid crystal panel, for forming an image. In this retardation material, two types of retardation regions having different retardation characteristics are regularly arranged to constitute a patterned retardation material. In the present specification, a retardation material thus patterned in which a plurality of retardation regions having different retardation characteristics is arranged is particularly called a patterned retardation material hereinafter.
The patterned retardation material can be fabricated by using a polymerizable liquid crystal that is a liquid crystal having polymerizability and optically patterning a retardation substance including the polymerizable liquid crystal as disclosed in Patent Document 2, for example. In the optical patterning of the retardation substance including a polymerizable liquid crystal, a photo-alignment technique known for forming an orientation material for a liquid crystal of a liquid crystal panel is used. Specifically, a coating film made of a material having photo-alignment properties is provided on a substrate, and two types of polarized beams having different polarization directions are radiated on this coating film. Thus, a photo-alignment film is obtained as an orientation material in which two types of liquid crystal alignment regions are formed and the directions of alignment control of liquid crystals in the regions are different. Onto this photo-alignment film, a retardation substance containing a polymerizable liquid crystal in a solution state is applied to perform alignment of the polymerizable liquid crystal. Subsequently, the polymerizable liquid crystal thus aligned is cured to form a patterned retardation material.
As materials having photo-alignment properties that can be used in orientation material formation using a photo-alignment technique for liquid crystal panels, an acrylic resin and a polyimide resin, for example, are known that have in a side chain thereof a photodimerizable moiety such as a cinnamoyl group and a chalcone group. It is disclosed that these resins exhibit a property of controlling alignment of liquid crystals (hereinafter, also called liquid crystal alignment properties) by polarized UV irradiation (see Patent Document 3 to Patent Document 5).
As described above, in order to obtain a patterned retardation material, an orientation material is formed by employing a photo-alignment technique. In one known method for forming an orientation material, irradiation is conducted with two types of polarized light whose polarization directions are different. In such a method, a photomask is used in a first step of exposing to polarized light, and for example, out of the two types of retardation regions, only a first region of a coating film for forming a first retardation region is irradiated with first polarized light having a specific polarization direction, with a first amount of irradiation. Subsequently, in a second step of exposing to polarized light, the photomask is removed, and the whole area of the coating film including a second region of the coating film for forming a second retardation region is irradiated with second polarized light having a polarization direction that is different from that of the first polarized light, with an amount of irradiation less than the first amount of irradiation, such as with the one-half amount of the first amount of irradiation.
In another method, the whole area of a coating film is irradiated with a first polarized light in a first step of exposing to polarized light, with a first amount of irradiation. Subsequently, in a second step of exposing to polarized light, a photomask is used, and for example, out of the two types of retardation regions, only a first region of a coating film for forming a first retardation region is irradiated with second polarized light having a polarization direction that is different from that of the first polarized light, with an amount of irradiation more than the first amount of irradiation, such as with the amount of twice of the first amount of irradiation.
FIGS. 2A and 2B are figures illustrating a conventional method for manufacturing an orientation material. FIG. 2A is a figure illustrating a first step of exposing to polarized light, and FIG. 2B is a figure illustrating a second step of exposing to polarized light.
As shown in FIGS. 2A and 2B, a method called a mask alignment method has been known as another method for manufacturing an orientation material.
In the mask alignment method shown in FIGS. 2A and 2B, a step of exposing to polarized light is conducted at least two times, and every time a photomask having a pattern different is used.
Specifically, in the mask alignment method, firstly a coating film 1001 made of a material having photo-alignment properties is provided on a substrate 1000 that serves as a supporting material. A photomask 1002 is used in a first step of exposing to polarized light, and for example, out of the two types of retardation regions in a retardation material, only a first region of the coating film 1001 for forming a first retardation region is irradiated with first polarized light 1004 having a specific polarization direction, with a first amount of irradiation. Subsequently, in a second step of exposing to polarized light, a photomask 1003 having a different pattern is used. After positioning, only a second region of the coating film 1001 for forming a second retardation region in the retardation material is irradiated with second polarized light 1005 having a polarization direction that is different from that of the first polarized light 1004. The amount of irradiation of the second polarized light 1005 can be comparable to that of the first polarized light 1004, and thus exposure steps with polarized light irradiation is made efficient.
However, for this prior art technique, the mask alignment method, two photomasks have to be prepared, and the mask alignment is highly difficult to perform, and thus yield is expected to be low.